1. Field of the Invention
The present invention relates to a micrometer which can electrically make a digital display of measured results.
The latest trend in micrometers is to design them such that the measured results can be digitally displayed. In some micrometers designed for digital display of measured results, the spindle movement is mechanically converted to a rotation, which drives a mechanical counter to make a digital display of measured results; and in others, the spindle movement is converted to an electrical signal, which causes an arithmetic circuit to drive an electric counter to make a digital display of measured results.
2. Description of the Prior Art
In a micrometer equipped with a mechanical counter for digital display, the rotation of the spindle is transmitted by gear and pinion for successive rotation of letter gears on the mechanical counter for digital display. In the micrometer of this type, however, the system for transmitting the spindle movement to the letter gears of the counter consists only of gearing; and because of limitations to the possibilities of enhancing the gear accuracy through elimination of backlash and slackness in the support of gear shaft, there is a limitation to improving the accuracy of readings.
It is for this reason that a micrometer has been developed which can give accurate readings of measured results as an electrical signal to which the spindle movement is converted.
For conversion of the spindle movement to an electrical signal, a differential transformer is utilized. For instance, a coil is attached to the micrometer body; the core member is made movable together with the spindle; and thus the coil can produce an electrical signal output proportional to the spindle movement. Such a micrometer is disclosed in the U.S. Pat. No. 3,924,336.
In another type of micrometer, a glass scale, a light-receiving element and a light-emitting element are combined or two discs with rotational shafts being eccentric to each other are installed, whereby the light-receiving element and the light-emitting element at their overlap portion yield an electrical signal. Such a micrometer is disclosed in the British Pat. No. 1,400,293.
In still another type, the readings of a displacement of a linear-variable scale are converted to an electrical signal, such being disclosed in the U.S. Pat. No. 4,062,120.
As mentioned above, several micrometers for electrical display of measured results have been proposed, but as a matter of fact they are not yet practically used, because it is difficult to incorporate electrical parts in them without deteriorating their performance.